Revert NULL move beta corrections

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 92d2c75ed2c6fd5a3ff3b89d376e60c704c048f4..549f19e211caecc575a10eb6fda327a6986e1d06 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -149,16 +149,6 @@ namespace {
   // evaluation of the position is more than NullMoveMargin below beta.
   const Value NullMoveMargin = Value(0x300);
 
-  //Null move search refutes move when Nullvalue >= Beta - Delta. Index is depth
-  //in full plies. Last index is 9+.
-  const Value NullMoveDeltaMidgame[] =
-    { Value(-8), Value( 6), Value(-15), Value( 9), Value(21),
-      Value(34), Value(54), Value( 59), Value(61), Value(61) };
-
-  const Value NullMoveDeltaEndgame[] =
-    { Value( 6), Value( 0), Value(-13), Value(-9), Value(-35),
-      Value(12), Value(24), Value(  9), Value( 5), Value(  5) };
-
   // Pruning criterions.  See the code and comments in ok_to_prune() to
   // understand their precise meaning.
   const bool PruneEscapeMoves = false;
@@ -1207,19 +1197,13 @@ namespace {
         &&  ok_to_do_nullmove(pos)
         &&  approximateEval >= beta - NullMoveMargin)
     {
-        //Calculate correct delta. Idea and tuning from Joona Kiiski.
-        ScaleFactor factor[2] = { SCALE_FACTOR_NORMAL, SCALE_FACTOR_NORMAL };
-        Phase phase = pos.game_phase();
-        int i = Min(depth / OnePly, 9);
-        Value delta = scale_by_game_phase(NullMoveDeltaMidgame[i], NullMoveDeltaEndgame[i], phase, factor);
-
         ss[ply].currentMove = MOVE_NULL;
 
         StateInfo st;
         pos.do_null_move(st);
         int R = (depth >= 4 * OnePly ? 4 : 3); // Null move dynamic reduction
 
-        Value nullValue = -search(pos, ss, -(beta-delta-1), depth-R*OnePly, ply+1, false, threadID);
+        Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
 
         pos.undo_null_move();
 
@@ -1227,7 +1211,7 @@ namespace {
         {
             /* Do not return unproven mates */
         }
-        else if (nullValue >= beta - delta)
+        else if (nullValue >= beta)
         {
             if (depth < 6 * OnePly)
                 return beta;